A nutritionally defective E.coli strain grows only on meduim containing thymine, whereas another nutritionally defective strain grows only on meduim containing leucine. When these two strains are grown together , a few progeny are able to grow on minimal meduim with neither leucine nor thymine. How can this result be explained?
E. coli that can only grow on medium containing thymine are called thymine auxotrophs (thy-).
E. coli that can only grow on medium containing leucine are leucine auxotrophs (leu-).
Obviously, thy- is wild-type in all other genes; therefore, they are really thy-/leu+.
Same logic applies for the leucine auxotrophs. They are really thy+/leu-.
But how can a wild-type bacteria come out of this mixture? ...